[Originally published before the ruling; text and headline updated to reflect it. – Ed.]

The Supreme Court is considering the case Maryland v. King (thanks to Jennifer Wagner at Genomics Law Report for an excellent and detailed analysis), which turns on whether law enforcement needs a warrant to take the DNA of someone arrested and charged with, but not yet convicted of a crime. Maryland AG Douglas Gansler has argued to NPR that the privacy intrusion involved is negligible:

“They’re presumed innocent when they’re handcuffed; they’re presumed innocent when they’re strip-searched; and they’re presumed innocent when they’re sitting in jail awaiting trial,” he observes. “Those are far greater invasions of privacy than touching a Q-tip to the inside of your cheek for a second.”

The cheek swab taken from Mr. King came up with a hit for a six-year-old rape case. King was convicted of that charge, and is serving life in prison. King’s attorney, Kannon Shanmugam, argues that the intrusiveness of the search comes from the fact that the search was capable of disclosing a wide array of deeply personal information, and was taken at a time when his client had not been charged with any crime:

“The default rule under the Fourth Amendment is that when a search takes place, it has to be supported either by a warrant issued by a magistrate or by some level of individualized suspicion”

In this case, two very different conceptions of the Fourth Amendment collide. It was once the case that the physical intrusiveness of a search more or less tracked with the amount of information about the arrestee that the search would disclose. Fourth Amendment jurisprudence built up a careful set of rules regarding stops, patdowns and strip-searches, each of which would disclose more than the last and received correspondingly more careful scrutiny.

That relationship is now breaking down. People with smartphones carry their whole lives in a readily searchable object in their pocket, and searching that object is, in all ways but the physical, more intrusive than a strip search. Here, Gansler argues that because a cheek swab is easily taken and doesn’t even properly penetrate the body, it deserves less Fourth Amendment protection; Shanmugam argues that because the cheek swab can disclose information on which his client’s freedom may turn, it deserves the highest Constitutional protection. The same philosophy pervades discussion of the Fourth Amendment for other digital searches and seizures. The thinking goes, if it is easy to search for and seize a given set of personal information, is it really subject to the Fourth Amendment?

If the Supreme Court resolves the current circuit split over arrestee DNA collection, analysis, and aggregation in a nationwide DNA database in favor of allowing suspicionless DNA collection from arrestees to continue, then participating states should adopt measures requiring automatic expunction of the DNA records of any arrestees who are not convicted of the crime they were arrested for prior to the DNA collection within a reasonable time period.

This shows that if the Supreme Court rules against protecting arrestees’ DNA with a warrant, the best that Fourth Amendment activists can hope for out of the ruling is a “no harm, no foul” rule. But the Constitutional problem does not stem solely from the fact that the government retains the data after it collects it without a warrant and without probable cause to believe that the person whose DNA it is is involved with a crime.

If we concede that point, then we have given license to law enforcement to keep as large a file on all of us as it likes, just because it is easy for it to collect the information. Relative to a DNA swab, digital records about us are often as easy to collect as a Google search. It’s technically straightforward for the NSA or other law enforcement authorities to intercept and record all phone calls passing through a phone company switching station, as they’re planning to do here in Massachusetts. Ease of collection is not the proper criterion for whether the Fourth Amendment applies, because now vast amounts of data on a person can be collected without even being in their presence.

It’s not OK for the government to have records on everybody, whether or not they’re suspected of a crime. It doesn’t make it notably better if the government has some protocol for refreshing their unconstitutionally collected information about us from time to time. I don’t find that prospect comforting.

UPDATE: And the ruling is in; 5-4 in favor of the constitutionality of collecting DNA from arrestees. Justice Kennedy wrote for the majority, consisting of him, Roberts, Alito, Thomas and Breyer. Scalia composed an extraordinarily powerful dissent. The ruling and dissent can be read in full here.